1. Field of the Invention
This invention relates to a pattern forming method by photolithography and a method of manufacturing an ink jet recording head to which the aforementioned method is applied.
2. Description of Related Art
In recent years, techniques of forming a three-dimensional structure of the order of micron which are typified by MEMS has been actively studied. As typical one of them, mention may be made of a method using a photosensitive resin capable of forming a pattern of a high aspect ratio. In the conventional method, however, it has been difficult to control the edge shape of a pattern opening portion and the taper angle of the wall surface of a pattern recess at a time. That, if the focus (imaging position) of the pattern by an exposing machine is set near the surface of a coat resin layer formed of the photosensitive resin, there can be obtained an edge shape in which the pattern opening portion is sharp, but it has been difficult to make the wall surface of the pattern recess into a tapered shape. Conversely, if the imaging position of the pattern by the exposing machine is offset (defocused) from the vicinity of the surface of the coat resin layer formed of the photosensitive resin, it becomes easy to make the wall surface of the pattern recess into a tapered shape, but it has been difficult to keep the pattern opening portion in a sharp edge shape.
Here, as an example of devices in which it is necessary to control the edge shape of the pattern opening portion and the taper angle of the wall surface of the pattern recess, mention may be made of the shape of the nozzle (ink discharge port) of an ink jet recording head in an ink jet recording system.
Heretofore, in the ink jet recording system, in order to made a recording characteristic higher in degree, there has been continued technical development for improvements in performance such as a smaller liquid droplet, a higher driving frequency and a greater member of nozzles. The applicant discloses, in Japanese Patent Application Laid-open No. H6-286149, a method of using a photosensitive material for a layer forming a nozzle, and realizing precise nozzle structure by photolithography technique as a method of manufacturing an ink jet recording head which satisfies the above-noted requirement.
The applicant further discloses, in U.S. Pat. No. 6,895,668, a manufacturing method of forming dry film or the like having photosensitivity as a nozzle surface processing material (a liquid repelling layer) on a material layer forming a nozzle.
Now, in the ink jet recording head, the taper angle of the nozzle greatly affects the discharging characteristic of ink in some cases, and generally it is regarded as being more advantageous to the discharging characteristic of ink to make the wall surface of the nozzle into a tapered shape. In the formation of a nozzle by photolithography, it is possible to defocus when pattern exposure is effected to thereby taper the nozzle. In the pattern exposure in the defocused state, however, there has been a case where the edge of the distal end of the nozzle (the opening portion of the ink discharge port) deviates from a proper focus and therefore tend to become rounded, and this has not been preferable in the discharging characteristic of ink.